This invention relates generally to the production of transparent, impact-resistant, thermoplastic resin compositions. More particularly, the invention relates to a novel process for producing methyl methacrylate-styrene resin compositions having excellent transparency and retaining impact resistance (impact strength).
Heretofore, it has been generally known that methyl methacrylate-styrene copolymers (hereinafter referred to as MS copolymers) have excellent transparency but have disadvantageously poor resistance to impact. Various attempts have been made to improve the impact resistance of these MS copolymers, but to date, solving this problem fully has been difficult.
As a result of our research, we have succeeded in obtaining:
(1) A GRAFT COPOLYMER (HEREINAFTER REFERRED TO AS AN MBS graft copolymer) obtained by adding a small quantity of a polyethylene oxide of high molecular weight to a rubber latex having as its predominant constituent of the rubber a diolefin monomer thereby to cause partial coagulation of the rubber latex and thereafter subjecting a monomer mixture of methyl methacrylate and styrene to post polymerization in the presence of the rubber latex, and
(2) A COMPOSITION OBTAINED BY MIXING THE ABOVE MENTIONED MBS graft copolymer and an MS copolymer.
In either of the above cases (1) and (2), a methyl methacrylate-styrene thermoplastic resin having excellent transparency and, at the same time, impact resistance was obtained.
A feature of this invention is that, in the step of adding the monomer mixture of methyl methacrylate and styrene to a conjugated diolefin polymer rubber latex or a copolymer rubber latex having a conjugated diolefin as a predominant constituent of the rubber in the production of an MBS graft copolymer in either of the above cases (1) and (2), a high molecular polyethylene oxide of an average molecular weight of 100,000 or more is added prior to, or at the time of, such addition step, for the post polymerization of the above mentioned monomer mixture to cause the rubber latex to partly coagulate thereby to impart impact resistance to the methyl methacrylate-styrene resin.
That is, we have found the above described feature affords the following possibilities. It is possible to obtain an impact resistance which is superior by far to that obtainable in an MBS graft copolymer produced from a rubber latex which has not been coagulated with a polyethylene oxide of high molecular weight. Furthermore, particularly in the production of an MBS graft copolymer, an MBS graft copolymer obtained from a rubber latex to which a polyethylene oxide having an average molecular weight greater than 100,000 has been added is superior in impact resistance to an MBS graft copolymer obtained from a rubber latex in which a polyethylene oxide of low molecular weight such as, for example, a polyethylene oxide ordinarily called a polyethylene glycol of a molecular weight of the order of 200 to 20,000, has been used. In addition, when a polyethylene oxide of high molecular weight is used according to this invention, a methyl methacrylate-styrene thermoplastic resin of impact resistance superior to those in cases where other high molecular weight coagulants such as polyvinyl alcohol and methylcellulose are used is obtained.
Furthermore, in the production of an MBS graft copolymer, as is known, the index of refraction of the resin varies depending on the composition of the rubber used.
At the time of post polymerization, however, the proportions of the methyl methacrylate and styrene can be so selected that the index of refraction of the post polymerizate approaches that of the rubber, and, also in the MS copolymer to be mixed with this MBS graft copolymer, the proportions of the methyl methacrylate and styrene can be selected to cause the index of refraction to approach that of the MBS graft copolymer in a simple manner. In this manner, it is possible to impart transparency to the resin.
The nature, utility, and further features of the invention will be apparent from the following detailed description beginning with a consideration of general details of the invention and concluding with specific examples of practice illustrating preferred embodiments of the invention.